1. Field
The present disclosure relates to nanoparticle multilayer films.
2. Description of the Related Art
Nanoparticle multilayer films refer to films with a plurality of nanoparticle layers stacked upon one another. Nanoparticle multilayer films may be used as, for example, semiconductor materials, optic materials, energy storing materials, magnetic materials, and magneto-optic materials.
A nanoparticle multilayer film may be formed in a layer-by-layer manner using quantum dots or nanoparticles of which the surfaces are modified to have charges. For example, quantum dots coated with positively charged polymers, and quantum dots coated with negatively charged polymers may be used to alternately coat a substrate to form a quantum dot (QD)-polymer composite material multilayer thin film. In another example, quantum dots that are surface-modified with cationic organic ligands or polymers, and quantum dots that are surface-modified with anionic organic ligands or polymers may be used to induce spontaneous layer-by-layer coating of the surface-modified quantum dots on their own due to the charges thereof. See, e.g., Nano Letters, 2004, 4 (8), pp 1421-1425.
In a nanoparticle multilayer film formed using such a method, an organic ligand or polymer could be present between nanoparticles and/or between nanoparticle layers. The presence of the organic ligand or polymer between the nanoparticles may cause an electrical insulation of the nanoparticle multilayer film and prevent a coupling of the nanoparticles due to an increased distance between the nanoparticles. It is known that coupling of nanoparticles does not occur when the nanoparticles are spaced apart from one another by a distance of about 1.8 nm or larger.
Thus, the nanoparticle multilayer films formed using nanoparticles that are surface-modified with organic ligands or polymers may perform poorly in some application fields where, for example, electric conductivity or coupling of nanoparticles is required.